The present invention relates to the work-up of a surfactant-containing reaction mixture arising as a microemulsion.
In many chemical reactions, the starting materials and, generally, also the products have solubilities so different that they can be dissolved together neither in one non-polar organic solvent nor in water. A typical example of this is the dehydrohalogenation of 3,4-dichloro-1-butene (water-insoluble) by sodium hydroxide which is added in the form of aqueous sodium hydroxide solution. Further examples are the formation of nitrites from alkyl halides and inorganic cyanides or various alkylation reactions in the presence of strong bases (Nachr. Chem. Techn. Lab. 40, (1992), 1344). The difficulties indicated can be counteracted, for example, as follows:
1. A polar organic solvent (for example methanol, dimethylformamide, acetonitrile) is used which dissolves both starting materials to a limited extent. The reaction then proceeds in a homogeneous phase. PA1 2. The starting materials are dissolved in their preferred solvents and a large internal interface is generated by a dispersion means (for example by agitators or nozzles). PA1 3. A phase-transfer catalyst is added to the starting materials dissolved in their solvents, which catalyst increases the solubility of one of the two reaction partners in the solvent of the other one. PA1 a) is subjected to a temperature change by 20 to 50K to lower or to higher temperatures and by this means a phase having a high surfactant content and a substantially surfactant-free phase are obtained, PA1 b) the phase which is substantially surfactant-free and contains reaction products is separated off and an aqueous phase separated off is replaced by the aqueous phase of the first reaction partner and an organic phase separated off is replaced by the organic phase of the second reaction partner, PA1 c) the reaction mixture to be treated is subjected to a second temperature change by 10 to 80.degree. C. in the opposite direction to the first temperature change and by this means, again, in addition to a phase having a high surfactant content, a substantially surfactant-free phase is obtained, PA1 d) the phase formed in c) which is substantially surfactant-free and contains reaction product is separated off and replaced in the manner mentioned under b) and PA1 e) the reactive mixture then present is again fed to the reaction. PA1 (i) The reaction mixture arising as ME reacted to completion is heated by 20 to 50K. In this case, in addition to the phase having a high surfactant content, a substantially surfactant-free phase forms. The fact of the formation of a substantially surfactant-free phase is a function of the type of the reaction partners, of their amounts, of the type and amount of surfactant used, thus quite generally of the composition of the ME, and of the temperature at which the reaction mixture reacted to completion arises and of the temperature to which it is brought by the temperature change according to the invention. Likewise a function of the said parameters is also the question of whether the substantially surfactant-free phase is an aqueous phase or a water-immiscible organic phase. In an analogous manner as described above, the substantially surfactant-free phase formed is separated off and replaced by a phase of the same type. This reaction mixture treated by temperature increase, phase removal and phase replacement is then subjected to a temperature reduction by 10 to 80K; again, in addition to a phase having a high surfactant content, a substantially surfactant-free phase forms. The type of the surfactant-free phase which forms in this second phase separation is of a different type (aqueous or organic) to the surfactant-free phase which has formed in the first phase separation. If, therefore, in the temperature elevation initially carried out, a surfactant-free organic phase had formed which had been replaced, in the temperature reduction a surfactant-free aqueous phase forms which is replaced, and vice versa. PA1 (ii) The reaction mixture arising as ME reacted to completion, in an opposite manner to the variant under (i), is initially cooled by 20 to 50K, with, depending on the composition of the ME and depending on the temperatures of the ME obtained and its cooling, in addition to the phase having a high surfactant content, only one substantially surfactant-free phase being formed which, in the meaning of the material described above, can be an aqueous or an organic water-immiscible phase. This substantially surfactant-free phase is separated off and replaced in the meaning of the material described above, whereupon the now newly formed mixture is heated by 10 to 80K. After this heating a substantially surfactant-free phase arises again which is of the opposite type to the substantially surfactant-free phase initially arising. This is also separated off and replaced in the meaning of the material described above. PA1 the etherification, PA1 the dehydrohalogenation of halogenated hydrocarbons by aqueous alkali metal hydroxide, for example the dehydrochlorination of 3,4-dichloro-1-butene with NaOH, PA1 the formation of nitrites from alkyl halides and inorganic cyanides, PA1 the alkylation of alcohols, phenols, carboxylic acids, amines or amides using alkyl halides in the presence of strong bases, PA1 the .alpha.-alkylation of activated compounds using halogenoalkyls, e.g. the formation of .alpha.-alkylated nitrites from nitrites and halogenoalkyls, PA1 hydrolyses of esters in the presence of strong bases, PA1 oxidations of organic substances by bleaching lye, PA1 oxidations of organic substances by oxygen in the presence of water-soluble catalysts, PA1 reductions by water-soluble catalysts, PA1 oxidations of organic substances by H.sub.2 O.sub.2 in the presence of water-soluble catalysts, PA1 oxidations by aqueous cerium (IV) sulphate solutions, PA1 acidic or alkaline eliminations of protecting groups. PA1 the dehydrohalogenation of halogenated hydrocarbons, PA1 the formation of nitrites from alkyl halides and inorganic cyanides, PA1 the alkylation of alcohols, phenols, carboxylic acids, amines or amides, PA1 the .alpha.-alkylation of activated compounds or PA1 the hydrolysis of esters.
However, the methods indicated generally have a disadvantage. Thus, polar organic solvents and phase-transfer catalysts are frequently environmentally polluting, for which reason it must be expected that their use will become increasingly more expensive owing to environmental restrictions and the necessity of a substantial work-up and therefore alternatives must generally be sought and found. The generation of a large phase interface by dispersion is generally only useful for rapid reactions, since in the case of slow reactions, because of the necessity of maintaining dispersions for a long period, much energy is required.
A novel method which does not have the disadvantages of the abovementioned methods is the generation of a microemulsion from the starting materials dissolved in their preferred solvents, by the addition of a surfactant (J. Am. Chem. Soc. 113 (1991), 9621). Such thermodynamically stable microemulsions contain highly fine droplets whose size is greatly below that of droplets generated by dispersion processes. Since the microemulsion forms spontaneously under certain conditions, that is is inherently stable, even slow reactions can be carried out particularly economically herein.
Whereas phase-transfer catalysts and dispersion processes are already used industrially, the use of microemulsion processes has, to date, not passed beyond the laboratory scale. This is due to the fact that microemulsions are only stable in a limited temperature range and concentration range of the starting materials. In order therefore to achieve stabilities sufficient for industrial use over a larger temperature range and to achieve an increase in starting material concentrations, increased surfactant concentrations are generally necessary. However, such increased surfactant concentrations in turn increase the necessity for work-up of such microemulsions, in order to recover substantially the surfactant used; this recovery at the same time prevents environmental pollution or corresponding countermeasures and, on the other hand, contamination of the product.